1. Field of the Invention
This invention relates to fixing structures for fixing screws that are used for adjustment on airtight closing of tone holes of tube bodies of woodwind instruments by key systems.
2. Description of the Related Art
In general, woodwind instruments such as flutes, oboes and clarinets have tube bodies whose tone holes are controlled to be opened or closed by key systems being operated by players. That is, players operate the key systems to selectively open or close the tone holes by shifting tampons in position, thus producing sounds having desired pitches. Due to leakage of air from the tone holes of the tube bodies, the woodwind instruments are varied in pitch, tone volume and tone color to cause deterioration of sound quality. In other words, if air leak from the tone holes of the tube bodies unintentionally against player""s operations of the woodwind instruments, unwanted variations are caused to occur in pitch, tone volume and tone color of sound being produced. In that case, the players have difficulties in handling the woodwind instruments to stabilize production of sound in a good quality, so it becomes difficult for the players to produce beautiful woodwind sounds having desired pitches. It is needless to say that mechanical performance of the woodwind instruments is greatly and directly influenced by materials of tampons and construction of the tampons being incorporated into key cups as well as positional adjustments of the tempons on the tone holes. Herein, the tampons are brought into tight contact with the tone holes to prevent noise from being produced and to close the tone holes in an airtight manner. To achieve preferable performance of the key system of the woodwind instrument, the tampons are made using prescribed base materials which are made by placing felts of high quality and pasteboards in layers, wherein the felts are subjected to compressed formation in prescribed thickness, which approximately ranges between 2 mm and 3 mm, for example. Concretely speaking, the tampons are made by coating the base materials with coating materials such as skins (e.g., sheep or calf leathers) and bladders (e.g., sheep or goat internal skins).
The key system for operating the tampons is mainly constructed by key pipes, key cup arms, key cups and adjustment screws. Herein, the key pipes are pivotally supported by shafts to freely rotate, and the key cup arms are fixed to the key pipes. The key cups are attached to tip end portions of the key cup arms to store the tampons therein. The adjustment screws restrict rotation of the key cup arms to adjust closing degrees of the tampons on the tone holes. In general, there are provided two types of the key systems, namely, a close key system and an open key system. The close key system normally closes the tone holes in a non-performance mode, so it selectively opens the tone holes upon manual operations made by the player. The open key system normally opens the tone holes in a non-performance mode, so it selectively closes the tone holes upon manual operations made by the player.
With reference to FIGS. 4A and 4B, a description will be given with respect to a conventional example of a fixing structure of an adjustment screw, which is applied to an open key system that normally opens tone holes of a tube body of a woodwind instrument. Namely, a reference numeral 1 designates a tube body, 2 designates a tone hole which is formed at a selected position on an exterior periphery of the tube body 1, 3 designates a shaft that is arranged outside of the exterior periphery of the tube body 1 and is also arranged approximately in parallel with an axial line of the tube body 1, 4 designates a key pipe whose internal hole engages with the shaft 3 in a free rotation manner, and 5 designates a key cup arm that is fixed to a selected position of the key pipe 4 by braze, wherein a key cup (or simply a cup) 7 is installed on a tip end portion of the key cup arm 5. In addition, a reference numeral 6 designates a tampon (or pad) that is stored in the key cup 7 and is moved to open or close the tone hole 2, and 8 designates a communicating plate that is fixed to a selected position of the shaft 3 in connection with the key cup arm 5, wherein the communicating plate 8 has a tapped hole 8a with which an adjustment screw 9 is to be engaged. The key cup arm 5 has a communicating bearing 10 to project downwardly toward a tip end of the adjustment screw 9. When the key cup arm 5 is rotated to close the tone hole 2 by the tampon 6, the adjustment screw 9 comes in contact with the communicating bearing 10 to restrict further rotation of the key cup arm 5. If the tampon 6 imperfectly closes the tone hole 2 with a relatively low degree of closing, air is to be leaked from the tube body 1 by way of the tone hole 2 so that sound is deteriorated in quality or varied in pitch. To make adjustment on the woodwind instrument, a human operator (or worker) rotates the adjustment screw 9 to slightly change a contact timing at which the communicating bearing 10 comes in contact with the adjustment screw 9. Thus, the woodwind instrument is adjusted such that the tampon 6 closes the tone hole 2 in an optimal condition of closing.
With reference to FIGS. 5A and 5B, a description will be given with respect to another example of the fixing structure of the adjustment screw, which is applied to a close key system that normally closes tone holes, wherein parts identical to those of FIGS. 4A and 4B are designated by the same reference numerals. In FIGS. 5A and 5B, a stopper 11 is fixed to a selected position of a key pipe 4 in connection with a communicating plate 8. Herein, the stopper 11 has a tapped hole 11 a with which an adjustment screw 9 is to be engaged. When a tampon closes a tone hole, a tip end of the adjustment screw 9 is pressed against the communicating plate 8 by elastic force being produced by a spring (not shown). In such a close key system, a human operator rotates the adjustment screw 9 to change an angle of the stopper 11 against the communicating plate 8. Thus, a woodwind instrument installing the close key system is adjusted such that the tampon closes the tone hole in an optimal condition of closing by adjustment of the angle of the stopper 11 against the communicating plate 8.
The conventional fixing structures of adjustment screws of the woodwind instruments bear drawbacks in that the adjustment screws are loosened or released during musical performance of the woodwind instruments. So, engineers or human operators conventionally take various measures for prevention of loosening of the adjustment screws, as follows:
(1) An end of the communicating plate 8 is partially slit to form a forked portion whose slit communicates with the tapped hole 8a with which the adjustment screw 9 is engaged. After the adjustment screw 9 is completely screwed into the tapped hole 8a, the forked portion of the communicating plate 8 is caulked so that an interior circumference of the tapped hole 8a is intensely pressed against the adjustment screw 9. Thus, frictional force (or rotation resistance) is increased between the tapped hole 8a and adjustment screw 9. The aforementioned stopper 11 is also modified as similar to the communicating plate 8.
(2) Melted synthetic resin material is applied onto the adjustment screw 9 and is then solidified to provide appropriate rotation resistance between the tapped hole 8a and adjustment screw 9.
(3) The adjustment screw 9 is excessively screwed into the tapped hole 8a by force to cause partial destruction of screw thread.
The aforementioned measures are conventionally adopted for the woodwind instruments, however, there is a room for further improvements for prevention of loosening of the adjustment screws during musical performance of the woodwind instrument. In the above, a first measure (1) teaches that a forked portion is formed by slitting an end portion of the communicating plate 8 and is caulked to increase rotation resistance between the tapped hole 8a and adjustment screw 9 so that the adjustment screw 9 will be prevented from being loosened. In such a first measure, however, if a human operator strongly caulks the forked portion of the communicating plate 8 too much, it becomes impossible to further rotate the adjustment screw 9 within the tapped hole 8a. In contrast, if the human operator weakly caulks the forked portion, it is impossible to apply sufficient rotation resistance between the tapped hole 8a and adjustment screw 9 so that the adjustment screw 9 is to be easily loosened. That is, the first measure bears a difficulty to set optimal rotation resistance between them. Due to caulking, the tapped hole 8a is elastically deformed in an elliptical shape, which may cause an error of coordination between the tapped hole 8a and adjustment screw 9. That is, as long as their axes match with each other or cross with each other at a right angle, the adjustment screw 9 well engages with the tapped hole 8a. Otherwise, the adjustment screw 9 is easily rotated and loosened from the tapped hole 8a. A second measure (2) teaches that the synthetic resin material is applied onto the adjustment screw 9 and is solidified to prevent the adjustment screw 9 from being loosened from the tapped hole 8a. Such a second measure merely provides temporary fixture because if the human operator repeats adjustment by repeatedly rotating the adjustment screw 9, the solidified synthetic resin material is partially peeled off and dropped to reduce an effect of prevention of loosening of the adjustment screw 9. In addition, it is difficult to apply an appropriate amount of the synthetic resin material onto the adjustment screw 9. Further, the human operator is required to have a good skill in application of the synthetic resin material onto the adjustment screw. A third measure (3) teaches that the adjustment screw 9 is prevented from being loosened from the tapped hole 8a by partial destruction of screw thread. However, the third measure bears a difficulty to produce appropriate rotation resistance between the tapped hole 8a and adjustment screw 9. If the human operator repeats adjustment by repeatedly trying the third measure, the key system bears a reduction of the effect of prevention of loosening of the adjustment screw as similar to the second measure.
It is an object of the invention to provide a fixing structure of screws for adjustment on airtight closing of tone holes of tube bodies of woodwind instruments by adopting a simple structure for certainly preventing adjustment screws from being loosened from tapped holes in key systems.
This invention provides a fixing structure that fixes an adjustment screw for use in adjustment of closing of a tone hole of a tube body of a woodwind instrument by a key system. The adjustment screw is fixed to a screw fixing member such as a communicating plate or a stopper having a tapped hole. A block that is made by synthetic resin material is formed in a prescribed shape having a prepared hole penetrating therethrough and is detachably attached to the screw fixing member. For example, the block is placed in an engagement channel of the stopper, then, the adjustment screw having an external thread is screwed into the prepared hole of the block to be tapped by force and is further rotated to engage with the tapped hole of the stopper. Herein, a tip end of the adjustment screw projects outside of the tapped hole of the stopper and comes in contact with the communicating plate. To prevent the block from being easily extracted or dropped from the engagement channel of the stopper, both of the block and engagement channel are formed in a trapezoidal shape in cross section. To prevent the adjustment screw from being easily loosened from the block, it is necessary to provide an appropriate amount of rotation resistance between the adjustment screw and the prepared hole of the block. For this reason, a hole diameter of the prepared hole of the block is set in proportion to an outer diameter d of the adjustment screw within a range between 0.85d and 0.95d.
If the rotation resistance is reduced due to aged deterioration or abrasion, the fixing structure can be easily repaired by merely changing the block with new one, wherein it is unnecessary to change the adjustment screw with new one because the adjustment screw is made by metal material such as stainless steel having sufficient hardness and durability.
According to this invention, it is possible to certainly prevent the adjustment screw from being easily loosened with a simple construction, and it is possible to secure maintenance for maintaining desired mechanical performance of the key system by merely changing the block with new one.